This invention relates to a multilayer printed circuit board (PCB) and, more specifically, to PCBs that are easily compensation adjustable.
Telecommunications and data transmissions systems are operating at higher and higher frequencies due to the huge increases in signaling traffic. Although known cables and wiring can, theoretically, handle such increased frequencies, one of the problems encountered is an increase in cross-talk as frequency of transmission is increased. At frequencies above, for example, one megahertz (1 MHz), the degradation of signals due to cross-talk becomes significant. One source of cross-talk is the electromagnetic radiation from the wire pairs in, for example, a transmission cable which induces unwanted signals, i.e., cross-talk, in adjacent pairs. The induced signals materially decrease signal-to-noise ratios and result in increased error rate in data transmission. Various arrangements have been used for reducing cross-talk in cables, such as shielding individual pairs, helically winding twisted pairs, or, where possible, increasing the physical separation of one pair from another.
Cross-talk also occurs in the station hardware, e.g. connectors, line terminals, splitters, cable or cables, etc. The design of station hardware, and more particularly, the connectors therefor should include provisions for reducing cross-talk within the connectors themselves or for counteracting or canceling the cross-talk which is an inevitable product of most such connectors. The plugs and jacks that are commonly used in telecommunications equipment generally include up to eight wires (four pairs) that are necessarily oriented both parallel and close together, a condition that leads to excessive cross-talk at high frequencies.
Cross-talk in the connector is typically reduced or compensated by what are known as compensating traces. By drilling holes and adjusting the sizes of the compensation traces on the PCB, cross-talk can be compensated to a desired amount. Increasing the hole size decreases the amount of compensation of the PCB. This is possible since compensation is roughly related to the surface area of the compensating traces. Typically, multilayer PCBs have compensation traces which are randomly placed from layer to layer. Hence, to adjust the compensation of the board, many different holes may be drilled into the board. Consequently, the desired compensation is not easily obtained without damaging various components on the board (e.g. circuit traces). Hence, it is desirable to form a PCB which is easily compensation adjustable and not subject to damage by numerous drilled holes.
The present invention relates to a printed circuit board which is easily compensation adjustable. The invention provides a PCB having compensator traces which are directly above and parallel to each other. The PCB layers contain compensator traces which are aligned in planes such that the compensator traces are vertically or directly above and/or below each other. In other words, the compensating traces are aligned in a direction that is perpendicular to the respective planes. Thus, compensation can be effected in each of the various layers of the PCB by drilling one hole for each of the layers since the compensation traces are vertically aligned.
The above advantages and features of the invention will be more clearly understood from the following detailed description which is provided in connection with the accompanying drawings.